In a suspension system for a truck or other heavy duty vehicle, it is important to control the pitch of the axle as the axle oscillates with respect to the chassis. For the drive axle, it is important to maintain alignment of the drive train as the axle oscillates and to maintain the wheels in contact with the ground under all conditions. Similarly, with a steer axle, it is important to maintain the axle in alignment to ensure proper steering response and to also control the axle during oscillation, braking, and acceleration so that the operator has full control of the vehicle under all conditions.
Applicant has previously invented and patented suspensions which utilize a parallelogram structure for controlling and stablizing the axle. Some of these include U.S. Pat. No. 4,114,926; U.S. Pat. No. 4,132,432; and U.S. Pat. No. 4,181,323; the disclosures of which are incorporated herein by reference. These patents disclose air spring suspensions utilizing parallelogram structures of various types to stabilize the axle under all conditions of oscillation, braking, and acceleration. This arrangement offers many advantages over suspensions of the prior art, such as eliminating wheel hop and axle windup during emergency braking, as explained more completely therein. While these inventions are limited only by the scope of the claims, the preferred embodiments disclose suspensions for both drive axles and steer axles stabilized by a parallelogram.
Applicant has also designed and developed a suspension system for a tandem axle which incorporates a central elastomer spring disposed between two pivotally mounted torque arms such that loading of the vehicle pivots the torque arms and compresses the central elastomer spring. This invention is disclosed and claimed in U.S. Pat. No. 4,278,271, the disclosure of which is incorporated herein by reference. As explained more fully therein, the central elastomer spring provides a smooth ride and, at the same time, has sufficient resiliency to support substantial loads. Additionally, a major advantage of the central elastomer spring is that it may be easily removed and replaced, and is a less complicated structure requiring fewer parts and therefore is less expensive to manufacture and maintain. Another feature of the central elastomer spring suspension is that the load capacity of the suspension may be changed by simply removing the elastomer and replacing it with another having greater or less resiliency, as desired. Although the invention as disclosed in applicant's prior U.S. Pat. No. 4,278,271 is limited only by the scope of the claims, the preferred embodiment shown therein is a suspension adapted for use with a tandem axle vehicle such as a trailer with a non-powered, non-steerable axle/chassis arrangement.
In the suspension of the present invention, applicant has succeeded in combining the many advantages of parallelogram stabilization with the advantages of a suspension having a central elastomer spring for use with a drive axle and a steer axle. The first embodiment, which is adapted for use with a drive axle, has a first hanger assembly mounted at the forward end of the suspension, a second hanger assembly mounted at the rearward end of the suspension, a generally U-shaped axle seat mounted over the axle in an inverted orientation, and first and second torque arms pivotally mounted to and extending between the axle seat assembly and one of the hangers. A radius rod pivotally mounted to and extending between the forward hanger and the axle seat assembly along with the forward torque arm completes the parallelogram. The central elastomer spring is disposed beneath the axle and held in place between the torque arms by dowel pins extending into an axial hole in the spring, so that loading of the vehicle pivots the torque arms and compresses the spring. Tension rails bolt to and extend between the legs of the U-shaped axle bracket to prevent them from opening up under load. A shackle assembly pivotally mounts the rear torque arm to the rear hanger assembly to permit free vertical movement of the axle as controlled by the parallelogram. The bolts fastening the tension rods to the axle seat assembly extend inwardly sufficiently to contact each torque arm as it pivots away from the central spring to limit its movement and prevent inadvertent release of the central spring. Removal of these bolts and separation of the axle from the chassis releases the spring such that it can be lifted out by hand. One or more shock absorbers extend between the chassis and axle seat assembly to dampen axle movement.
A second embodiment is adapted for use with a steer axle and includes many of the same component parts as is used in the first embodiment for the drive axle. This adds to the versatility of applicant's invention by minimizing inventory required to manufacture and maintain both suspensions. In the second embodiment, a different axle seat assembly bolts to the top of the steering axle, with the same torque arms pivotally secured to and extending between front and rear hanger assemblies, as in the first embodiment. However, the central elastomer spring is disposed immediately above the steering axle, and set screws extend upwardly through the bottom of the axle seat assembly to limit torque arm movement and prevent release of the spring. The same radius rod is positioned inwardly of the forward torque arm to avoid interference with controls for the steering arm and also meet the reduced space limitations inherent in a steering axle suspension. Other components used are exactly the same as in the first embodiment.
In both embodiments, the central spring may be easily removed by loosening the bolts or set screws, as appropriate, elevating the vehicle to separate the axle from the chassis which also pivots apart the torque arms, and lifting the spring from between the torque arms and dowel pins. The spring may then be replaced and the suspension placed back in working condition by reversing the above procedure.